There are known ink jet printers to record images by ejecting droplets of ink from an ink jet recording head to a sheet of recording medium. Generally, the ink jet printers have a supply roller to feed recording media stacked on a paper supply tray into a printer main body. The paper supply tray is generally provided with a separation pad allocated to face the supply roller. The separation pad prevents several recording media from being grabbed on top of the other at a time and fed into the printer main body. The supply roller sends forth the recording media while pressing them against the separation pad. The separation pad holds the recording media in the paper supply tray with a frictional force, allowing an uppermost recording medium to be fed into the main body at a time.
The supply roller is made of an elastic material, such as rubber, so that it can produce a strong frictional force against the recording medium. This supply roller is, however, easily covered with powders (fine paper powder) peeled off from the recording medium, and gradually lowers its frictional force over repetition of the feeding operation. Having fed a certain number of recording media, the ink jet printers show a decline in the feeding performance, changing a feeding cycle and causing a paper-pick (jamming) problem. Especially, compact personal printers generally have their supply rollers outside the casings, and allow the dust from outside to stick to the supply roller.
A method to solve this drawback is disclosed in the prior art (see, for example, U.S. Pat. No. 6,932,523 and Japanese Patent Laid-open Publication No. 2003-137447). This method includes a cleaning operation to press the supply roller onto the separation pad, and rotate the supply roller a predetermined number of times (about 20 times), so as to remove paper powders and dust on the supply roller with the separation pad to recover the frictional force. Some ink jet printers with this type of cleaning function have a sensor to detect dirt (dust) on the supply roller, and start the cleaning operation when the sensor detects a dirty spot (see, for example, Japanese Patent Laid-open Publications No. 2000-141818 and No. 07-112556).
However, in the cleaning operation of the U.S. Pat. No. 6,932,523 and the publication No. 2003-137447, the supply roller is always rotated the same number of times, irrespective of the degree of dirt on the supply roller. This may end up in continuing the cleaning operation for an unnecessarily long period to waste time when the supply roller is not very dirty. When the supply roller is very dirty, on the contrary, the cleaning operation may last before the dirt is removed completely.
Although the publications No. 2000-141818 and No. 07-112556 disclose detecting dirt to start the cleaning operation, they are silent about how long the cleaning operation should be continued. Therefore, these publications do not cure the deficiency of the above prior art.